Diode laser fiber array for powder bed fabrication or repair

ABSTRACT

A method of forming a build in a powder bed includes emitting a plurality of laser beams from selected fibers of a diode laser fiber array onto the powder bed, the selected fibers of the array corresponding to a pattern of a layer of the build; and simultaneously melting powder in the powder bed corresponding to the pattern of the layer of the build. An apparatus for forming a build in a powder bed includes a diode laser fiber array including a plurality of diode lasers and a plurality of optical fibers corresponding to the plurality of diode lasers, each optical fiber configured to receive a laser beam from a respective diode laser and configured to emitting the laser beam; a support configured to support a powder bed or a component configured to support the powder bed at a distance from ends of the optical fibers; and a controller configured to control the diode laser fiber array to emit a plurality of laser beams from selected fibers of the diode laser fiber array onto the powder bed, the selected fibers of the array corresponding to a pattern of a layer of the build and simultaneously melt the powder in the powder bed corresponding to the pattern of the layer of the build.

BACKGROUND

The present technology relates generally to the use of a diode laserfiber array for Direct Metal Laser Melting (DMLM) for use in thefabrication or repair of components, more particularly components of agas turbine engine.

Additive manufacturing is a known technology that enables the“3D-printing” of components of various materials including metals,ceramics and plastics. In additive manufacturing, a part is built in alayer-by-layer manner by leveling metal powder and selectively fusingthe powder using a high-power laser or electron beam. After each layer,more powder is added and the laser forms the next layer, simultaneouslyfusing it to the prior layers to fabricate a complete component buriedin a powder bed. Additive manufacturing systems and processes are usedto fabricate precision three-dimensional components from a digitalmodel.

In making a build in current powder bed systems, the laser beam orelectron beam is used to scan a layer of powder to sinter and melt thedesired shape in the layers of the powder bed. The typical scanning timefor such systems per layer is in the range of 70-100 seconds. For someapplications, the build can require days of processing time. Oneapplication of DMLM is in the fabrication and repair of airfoils for gasturbine engines for aircraft. The geometries of the airfoils aredifficult to form using conventional casting technologies, thusfabrication of the airfoils using a DMLM process or an electron-beammelting process has been proposed. With the layers built upon oneanother and joined to one another cross-section by cross-section, anairfoil or portion thereof, such as for a repair, with the requiredgeometries, may be produced. The airfoil may require post-processing toprovide desired structural characteristics.

Another problem of laser scanning Direct Metal Laser Melting (DMLM)systems is rapid cooling rates that can lead to cracking of certainalloys during the additive manufacturing build process. Rapid coolingrates also present difficulties in obtaining desirable grain growth, forexample grain growth that is normal to the layer surface.

BRIEF DESCRIPTION

In accordance with one example of the technology disclosed herein, amethod of forming a build in a powder bed comprises emitting a pluralityof laser beams from selected fibers of a diode laser fiber array ontothe powder bed, the selected fibers of the array corresponding to apattern of a layer of the build; and simultaneously melting powder inthe powder bed corresponding to the pattern of the layer of the build.

In accordance with another example of the technology disclosed herein,an apparatus for forming a build in a powder bed comprises a diode laserfiber array comprising a plurality of diode lasers and a plurality ofoptical fibers corresponding to the plurality of diode lasers, eachoptical fiber configured to receive a laser beam from a respective diodelaser and configured to emitting the laser beam; a support configured tosupport a powder bed or a component configured to support the powder bedat some working distance from ends of the optical fibers; and acontroller configured to control the diode laser fiber array to emit aplurality of laser beams from selected fibers of the diode laser fiberarray onto the powder bed, the selected fibers of the arraycorresponding to a pattern of a layer of the build and simultaneouslymelt the powder in the powder bed corresponding to the pattern of thelayer of the build.

DRAWINGS

These and other features, aspects, and advantages of the presenttechnology will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1A schematically illustrates a diode laser fiber array for use withthe present technology;

FIG. 1B schematically illustrates another diode laser fiber array foruse with the present technology;

FIG. 1C schematically illustrates another diode laser fiber array foruse with the present technology;

FIG. 2 schematically illustrates a system for simultaneous melting of apowder bed layer by a diode laser fiber array according to an example ofthe present technology;

FIG. 3 schematically illustrates a fiber optic construction usable in adiode laser fiber array according to an example of the presenttechnology;

FIG. 4A schematically illustrates a fiber array usable with the systemaccording to the present technology; and

FIG. 4B schematically illustrates another fiber array usable with thesystem according to the present technology.

DETAILED DESCRIPTION

Referring to FIG. 1A, a diode laser array 101 (e.g., a diode laser baror stack) includes a plurality of diode lasers, or emitters, 103, eachemitting a beam of radiation 105. A plurality of cylindrical lenses 107are positioned between the diode lasers 103 and a plurality of opticalfibers 109 to couple each diode laser 103 to an optical fiber 109. Theoptical fibers 109 may be provided in a bundle 102 between the diodelaser array and the free ends of the optical fibers, as shown forexample in FIGS. 1A-1C. However, it should be appreciated that diodefiber laser arrays that do not use coupling optics may be used with thepresent technology, as discussed below.

Referring to FIG. 1B, the diode laser fiber array 101 may include lenses117 at the ends of the optical fibers 109. The lenses 117 may beconfigured to provide collimated laser beams 120 from the optical fibers109. Referring to FIG. 1C, the diode laser fiber array 101 may notinclude optics (e.g. a lens) between the diode lasers 103 and theoptical fibers 109 and the beams of radiation 105 may be received by theoptical fibers 109 in proximity to the diode lasers 103. The opticalfibers 109 may have lenses 117 at their respective ends. The lenses 117may be configured to provide a predetermined divergence to the laserbeams 120 emitted from the optical fibers 109. It should also beappreciated that instead of providing lenses that the ends of theoptical fibers 109 may be shaped to provide collimated or divergentlaser beams 120.

Referring to FIG. 2, the diode laser fiber array 101 directs laser beams120 from the optical fibers 109 into a powder bed 130 to simultaneouslymelt all of the desired powder in a layer. To generate a desiredpattern, for example of a repair or a component to be fabricated, therequired diode lasers 103 are turned on to affect the desiredsimultaneous melting from each fiber 109. The melting process time forthe desired pattern may be less than a second, which is at least twoorders of magnitude faster than current scanning processes.

The powder bed 130 may be provided on a component 150, for example anairfoil of a gas turbine engine of an aircraft, which is supported on asupport 170 to provide a repair to the component. Although the presenttechnology may be applicable to the repair function on components, itshould be appreciated that the present technology is applicable for theadditive manufacturing build of new make components. The powder bed maybe provided on the support 170 and the diode laser fiber array 101 usedto build or fabricate the component layer by layer.

The support 170 may be moved by an actuator or an actuator system 175that is configured to move the support 170 in the Z direction (i.e.normal to the powder bed 130) as shown in FIG. 2. The actuator oractuator system 175 may also be configured to move the support 170 inthe XY plane as shown in FIG. 2, although the support 170 is not movedin the XY plane during simultaneous melting of the powder bed from eachfiber 109. The actuator or actuator system 175 may be controlled bycontroller 135 that is configured to control the actuator or actuatorsystem 175 and the diode laser fiber array 101. The actuator or actuatorsystem 175 may include, for example, a linear motor(s) and/or hydraulicand/or pneumatic piston(s) and/or a screw drive mechanism(s) and/or aconveyor. As the diode laser fiber array 101 is capable ofsimultaneously melting all of the required powder in the layer for apattern, there is no need to move either the array 101 or the powder bed130 during melting, for example as is done with current systems in whicha laser beam or electron beam is used to scan a layer of powder.

The distance D between the array of optical fibers 109 (i.e. the ends ofthe optical fibers 109) and the powder bed 130 may be controlled bymoving the support 170 in the Z direction. The distance D may depend onthe type of laser beams 120 emitted by the optical fibers 109 (e.g.whether the laser beams 120 are collimated or divergent, and the amountof divergence), the average output power of each diode laser 103, thepulse energy of each diode laser 103, the pulse width of each diodelaser 103, and or the beam distribution (e.g. Gaussian, top hat, etc.).The ends of the optical fibers 109 may be located at, for example, about5 mm to about 150 mm, for example about 20 mm to about 80 mm above thepowder bed 130 so that any region of a layer of the powder bed 130 canbe melted at the same time by turning the required diode lasers 103 onat the same time.

The controller 135 controls the turning on and turning off of each diodelaser 103. The controller may also control the rate at which the powerof each diode laser 103 is reduced when turned off. The controller 135may turn each diode laser 103 on and off within a time frame of, forexample, about 5 to 15 milliseconds, or longer if needed. For a givenlayer of powder 130, for example above an airfoil to be repaired, thedesired laser diodes 103 are activated to melt the powder in the desiredshape per a CAD design, which may be input and/or stored in thecontroller 135. This process may be repeated as many times as necessaryto build up the required repair region. In the case of the system beingused to fabricate a component, e.g. an airfoil, the process is repeatedas many times as necessary to build the component. The controller 135controls the actuator or actuator 175 to move the support 170 downwardlyas layers of powder are added and subsequently processed by the diodelaser fiber array. Each layer formed may be, for example, about 1 μm toabout 1 mm thick. In the case of repair of an airfoil, each layer may beformed, for example, about 100 μm thick.

The controller 135 may be a computer processor or other logic-baseddevice, software components (e.g., software applications), and/or acombination of hardware components and software components (e.g., acomputer processor or other logic-based device and associated softwareapplication, a computer processor, or other logic-based device havinghard-wired control instructions, or the like).

The diode laser fiber array 101 may be controlled by the controller 135to control the heat of powder near or adjacent to the melted region tocontrol the cooling rate of the melted region. The controller 135 mayalso control the diode laser fiber array 101 to preheat the powder bed130 and/or the component 150. The pre-heating power densities of thediode lasers 103 may be from about 100-100,000 watts/cm². By pre-heatingthe powder bed 130 and/or the component 150 and/or heating the regionnear or adjacent to the melt region, the thermal gradient may becontrolled to be substantially only in the direction normal to thepowder bed (i.e. in the Z direction in FIG. 2). This may help withmaterials that are crack sensitive to fast solidification cooling rates.Desirable grain growth that's normal to the layer surface may beachievable with planar cooling of a powder bed layer. This allowsformation of a directionally solidified (DS) type grain structure and asingle crystal structure with the build repair of an airfoil typestructure. It should also be appreciated that the diode lasers 103 maybe controlled to superheat the powder bed 130 to control the viscosityof the melted region. Controlling the viscosity of the melted regionallows control over, for example, evaporation of the powder, the grainstructure of the solidified layer, and/or the surface finish of therepair or component.

The material in the powder bed 130 may be metal powder, for example,CoCrMo powder. It should be appreciated that other materials, forexample plastic, ceramic, or glass, may be used for the powder bed.Depending on the material in the powder bed, the power of each diodelaser 103 may be from about 10 to about 60 watts. The power of the diodelasers 103 that are used may be related to the diameter of the opticalfibers 109 used. The power density of the diode lasers 103 may be up toabout 1,000,000 watts/cm² for melting the powder within a layer fromeach fiber.

The fiber centering position in the fiber array (e.g. as shown in FIGS.4A and 4B) is set by the diameter of a buffer, or coating 115 of theoptical fiber 109. Referring to FIG. 3, the optical fiber 109 comprisesa core 111, formed of for example silica, and cladding 113, formed forexample of silica, around the core 111. In order to create a numericalaperture and provide total internal reflection within the fiber 109, therefractory index of the silica core may be larger than the refractoryindex of the silica cladding. For example, the silica core may have arefractive index of about 1.45 and the silica cladding may have arefractive index of about 1.43. The cladding 113 may have a thickness ofabout 10 μm.

The buffer, or coating, 115 surrounds the cladding 113 and may be formedof, for example, acrylate. To reduce the center spacing between theoptical fibers 109, the buffer (acrylate coating) 115 may be replaced bya thinner acrylate coating to reduce the overall fiber diameter. Thethickness of the buffer, or coating 115 may be about 62 μm. The totaldiameter of the fiber 109 may be about 200 μm to about 250 μm.

The diameter of the fiber core 111 may be about 105 μm. It should beappreciated that fiber core diameters of about 60 μm may be used. Inaddition, it should be appreciated that optical fibers 109 of variouscross sections, may be used. For example, square fibers may be used toincrease fiber packing. The melt pool size produced by the laser beam(s)120 from each optical fiber 109 corresponds to the effective laser spotsize produced by the laser beam(s) 120. In the case of collimated laserbeams 120, the melt pool size corresponds generally to the diameter ofthe fiber core 111. However, the laser beams 120 from the fibers 109 maybe controlled to produce a melt pool size that is, for example, two tofour times as large as the diameter of the fiber core 111. The laserbeams 120 may be controlled to have a divergence to provide a melt poolsize larger than the diameter of the fiber core 111. In the case ofdivergent laser beams 120, the distance D from the ends of the fibers109 of the array 101 to the powder bed 130 will also influence the meltpool size of each fiber. The pulse width of the laser beams and thelaser beam profiles may also be controlled to adjust the melt pool sizeprovided by each fiber.

Referring to FIGS. 4A and 4B, the array of fibers 109 may be linear asshown in FIG. 4A or closed packed arrangement as shown in FIG. 4B. Otherarrays, for example hexagonal, may be used. It should also beappreciated that the array may be in a shape corresponding to the shapeof a component to be fabricated. The spacing between the fibers 109 maybe equal to the diameter of the buffer, or coating, 115.

The diode laser fiber array of the present technology may be used toprocess a powder bed layer by exposing the layer with simultaneous laserenergy from required diode laser beam sources. The present technologyalso allows melting the complete pattern in the layer in one time framethat could be less than a second and, when required, control the heat ofthe powder near and/or adjacent to the melted region to control thecooling rate of the melted region. The diode laser fiber array allowspermits grain structure control. The commercial advantages for diodelaser fiber array systems include fewer required systems to produce thesame amount of parts as current systems and tailoring power bed systemsto the size of the parts of interest. The technology disclosed hereinmay also be used to perform sintering, for example direct metal lasersintering.

It is to be understood that not necessarily all such objects oradvantages described above may be achieved in accordance with anyparticular example. Thus, for example, those skilled in the art willrecognize that the systems and techniques described herein may beembodied or carried out in a manner that achieves or optimizes oneadvantage or group of advantages as taught herein without necessarilyachieving other objects or advantages as may be taught or suggestedherein.

While only certain features of the present technology have beenillustrated and described herein, many modifications and changes willoccur to those skilled in the art. It is, therefore, to be understoodthat the appended claims are intended to cover all such modificationsand changes.

1. A method of forming a build in a powder bed, comprising: emitting aplurality of laser beams from selected fibers of a diode laser fiberarray onto the powder bed, the selected fibers of the arraycorresponding to a pattern of a layer of the build; and simultaneouslymelting powder in the powder bed corresponding to the pattern of thelayer of the build.
 2. A method according to claim 1, furthercomprising: controlling at least one of a duration of each laser beam, apulse energy of each diode laser, a pulse width of each diode laser, anaverage output power of each diode laser, an energy distribution of eachlaser beam, power density of each laser beam, a rate of reduction of thepower of each laser beam, and/or a distance of ends of the fibers fromthe powder bed.
 3. A method according to claim 2, wherein the averageoutput power of each diode laser is up to about 60 W.
 4. A methodaccording to claim 2, wherein the average output power of each diodelaser is between about 2 W to about 60 W.
 5. A method according to claim2, wherein the power density of each laser beam is about 1,000,000W/cm².
 6. A method according to claim 2, wherein the distance of ends ofthe fibers from the powder bed is between about 5 mm to about 150 mm. 7.A method according to claim 2, wherein the energy distribution of eachlaser beam is Gaussian or a top hat.
 8. A method according to claim 1,wherein the powder is metal, ceramic, glass or plastic.
 9. A methodaccording to claim 1, further comprising: emitting laser beams fromfibers at least adjacent to the pattern of the layer; and heating thepowder adjacent to the powder of the layer of the build to control acooling rate of the melted powder.
 10. A method according to claim 9,wherein heating the powder adjacent to the powder of the layer comprisesheating the powder at least one of prior to and/or during and/or aftersimultaneous melting of the powder of the pattern of the layer.
 11. Amethod according to claim 9, wherein a power density of the laser beamsheating the powder adjacent the pattern is in a range of from about 100W/cm² to about 100,000 W/cm².
 12. A method according to claim 1, whereina thickness of each layer is between about 1 μm to about 1 mm.
 13. Amethod according to claim 12, wherein a thickness of each layer is about100 μm.
 14. A method according to claim 1, wherein the build is a repairof a component.
 15. A method according to claim 14, wherein thecomponent is a turbine component.
 16. A method according to claim 15,wherein the turbine component is an airfoil.
 17. A method according toclaim 1, wherein the build is a component of a turbine.
 18. A methodaccording to claim 17, wherein the component is an airfoil.
 19. A methodaccording to claim 1, further comprising: repeating the emitting andsimultaneous melting to form a plurality of layers of the build.
 20. Amethod according to claim 1, further comprising: allowing the meltedpowder to cool and solidify.
 21. A method according to claim 1, furthercomprising: moving the selected fibers and the powder bed relative toeach other; and simultaneously controlling the diode lasers of theselected fibers during relative movement.
 22. An apparatus for forming abuild in a powder bed, comprising: a diode laser fiber array comprisinga plurality of diode lasers and a plurality of optical fiberscorresponding to the plurality of diode lasers, each optical fiberconfigured to receive a laser beam from a respective diode laser andconfigured to emit the laser beam; a support configured to support apowder bed or a component configured to support the powder bed at adistance from ends of the optical fibers; and a controller configured tocontrol the diode laser fiber array to emit a plurality of laser beamsfrom selected fibers of the diode laser fiber array onto the powder bed,the selected fibers of the array corresponding to a pattern of a layerof the build and simultaneously melt the powder in the powder bedcorresponding to the pattern of the layer of the build.
 23. An apparatusaccording to claim 22, wherein the controller is further configured tocontrol at least one of a duration of each laser beam, a pulse energy ofeach diode laser, a pulse width of each diode laser, an average outputpower of each diode laser, an energy distribution of each laser beam,power density of each laser beam, a rate of reduction of the power ofeach laser beam, and/or a distance of ends of the fibers from the powderbed.
 24. An apparatus according to claim 22, wherein the controller isfurther to control the diode laser fiber array to emit laser beams fromfibers adjacent to the pattern of the layer and heat the powder adjacentto the powder of the layer of the build to control a cooling rate of themelted powder.
 25. An apparatus according to claim 24, wherein thecontroller is configured to control the diode laser fiber array to heatthe powder adjacent to the powder of the layer at least one of prior toand/or during simultaneous melting of the powder of the pattern of thelayer.
 26. An apparatus according to claim 22, wherein the opticalfibers are provided in a plurality of linear arrays.
 27. An apparatusaccording to claim 26, wherein the plurality of linear arrays arearranged in closed packed configuration.
 28. An apparatus according toclaim 22, wherein each optical fiber comprises a core, a claddingsurrounding the core, and a buffer surrounding the cladding.
 29. Anapparatus according to claim 28, wherein the core and the cladding areformed of silica, and a refractive index of the core is larger than arefractive index of the cladding.
 30. An apparatus according to claim29, wherein a diameter of the core is from about 60 μm to about 105 μm.31. An apparatus according to claim 30, wherein a thickness of thecladding is about 10 μm.
 32. An apparatus according to claim 31, whereinthe buffer is formed of acrylate or polyimide.
 33. An apparatusaccording to claim 32, wherein a thickness of the buffer is about 62 μm.34. An apparatus according to claim 28, wherein a diameter of eachoptical fiber is about 250 μm.
 35. An apparatus according to claim 22,wherein the fibers have circular cross sections.
 36. An apparatusaccording to claim 22, further comprising: at least one lens, the atleast one lens being configured to collimate the laser beams.
 37. Anapparatus according to claim 22, further comprising: at least one lens,the at least one lens being configured to provide a predetermineddivergence to each of the laser beams.
 38. An apparatus according toclaim 22, further comprising: an actuator configured to move thesupport, wherein the controller is configured to control the actuator toadjust the distance between the powder bed and the ends of the opticalfibers.